Are known (EP 1143416 A2 Oct. 10, 2001) methodologies for attenuating noise in the time domain for transmission of acoustic signals. This noise suppression allows for better quality of communication in a noisy environment, but does not establish a full-duplex communication for more than two people.
Are known the “walkie-talkie” terminals to create independent networks of portable transceivers, for radio conversation or communication. Except with the use of multiple channels simultaneously, these products do not allow “conference” mode for more than two terminals.
Other types of voice transmission networks are using Bluetooth (registered trademark) technology, the DECT (Digital Enhanced Cordless Telephone), or Wi-Fi (set of communication protocols covered by the of IEEE 802.11 standards, ISO/IEC 8802-11) (trademark) or other protocols and radio bands to enable a conversation in “conference” mode for at least three people through mixer or concentration and redistribution technologies, or time division multiplexing protocols using a dedicated terminal acting in “Master” mode, the other acting in “Slave” mode. In all cases of systems allowing the “conference” mode for more than two terminals, the methods used are facing the need to define a terminal as “Base” or “Master” to mix and/or synchronize the data streams of the other terminals, or use multiple radio channels simultaneously. Some of these systems (FR 2947124 A1 of 24 Dec. 2010) when allowing a shared audio communication using time-division multiplexing on the same radio channel, and thus a conversation in “conference” mode, have the disadvantage of not being able to get rid of the Master terminal without compromising the communication between the other terminals. Thus, losing the radio signal coming from the Master Terminal, out of range or in default, condemns the communication between the other terminals or requires the reconfiguration of one of them in Master mode, this reconfiguration not being always possible without a complex manipulation.
Some techniques used to implement the designation of a single synchronization master on a regular basis in a network of asynchronous passive nodes, using a voting protocol in which each node self eliminates by ceasing transmission of sync frames when it receives a frame with a higher priority than itself (EP 2244526 A2 of 20 Oct. 2010). This technique requires high bit rates and requires in addition the retransmission of the resynchronization frames received from the master by each node to propagate them to all nodes of the network: it is therefore not applicable for use in a synchronous communication context between nodes which is necessary for audio communication in “conference” mode in a time division multiplex mode.
Some other solutions using a master/slave architecture based on time division multiplexing offer the automatic designation of a master when a device receives data frames but not the master ones (GB 2362292 Nov. 14, 2001). These solutions solve the case where the master disappears completely (extinction, breakdown, . . . ), but not the very common case where only some terminals are out of reach of the Master, as they allow the automatic enrollment of a second Master for out of reach terminals, the network then having with two non-necessarily synchronous masters, and thus two time references for time division multiplexing: the operation is then blocked because it goes against the very principle of said time division multiplexing. In this situation, the continuity of communication cannot be guaranteed as there is not ONE synchronized network, but TWO independent networks transmitting on the same radio frequency and creating collisions of data frames.
Other solutions using a master/slave configuration based on time division multiplexing offer automatic reconfiguration of terminals (EP 1843326 Oct. 10, 2007) to replace the master becoming faulty (out of range, extinction, . . . ). These solutions enable the network to automatically set a new synchronization master but also partially respond to the problems encountered in the field: for example, the case where only some terminals are out of reach of the master but at reach of each other is not supported although extremely common. This solution presents the first disadvantage of causing a failure of communication during reconfiguration, terminals via a state of “sleep” in order to synchronize with the new “Master”. As a second major drawback: the establishment of a new Master generates a second autonomous network disrupting communications of the first one.
Thus, in the present state of the art, any terminal being part of a “full-duplex” network on a single channel must be connected (within range) with THE “Master” terminal or THE “Base” to be able to communicate with the other terminals: so it is impossible to guarantee the continuity of communication between terminals within range of each other without depending on the communication of each of them with a “master” or “base” terminal.